This invention relates to a plate-type filter press which includes a plurality of vertically oriented filter plates each being horizontally shiftably supported on at least one guide carrier of the press frame. The filter press has a plate shifting apparatus which includes a traveling carrier element movable back and forth by means of a drive between a closed side of the filter press and an open side thereof. On the traveling carrier element there are mounted filter plate engaging elements adapted to engage a projection forming a fixed part of each filter plate for shifting the plates individually and in succession towards the open side of the filter press.
In plate-type filter presses of the above-outlined kind, where the filter plates are relatively large and thus the weight of the individual filter plates is significant, the shifting of the individual filter plates (for example, for ejecting the filter cake after completion of a filter process) can be effected only by means of a motor-power assisted plate shifting arrangement. If it is a desideratum to achieve short-period plate shifting steps, the shifting and return speeds of the plate shifting arrangement have to be high. Inherently, high shifting speeds lead to large accelerations and thus involve large accelerating forces affecting the individual filter plate that undergoes shifting. In addition to high-power moving mechanisms, such accelerating forces require stable and thus expensive suspensions and guides for the filter plates. Further, the operation of such filter presses involves substantial noise as the shifted filter plate collides with the outermost plate of the filter plate stack to which the plate has been moved. Further, such collisions lead to a significant wear of the filter cloth.
Further, the use of such filter press in special environments, particularly in the filtration of waste water sludge, involves the problem that after a while, the filter cloths become clogged, resulting in a significant deterioration of their efficiency. For a mechanical cleaning of the filter cloths, the latter are exposed to water jets of high pressure. For this purpose, washing pipes are used which have a number of spray nozzles. The length of the pipes generally corresponds to the width of the filter plate or, in some particular cases, to the height thereof. For performing the cleaning operation, the filter plates are, one-by-one, shifted away from the filter plate stack and positioned such that they are flanked by free space on both sides. The washing pipes are moved slowly either vertically, for example, from above downwardly or horizontally from one side to another, while cleaning water is ejected under high pressure from the nozzles onto the filter cloth to be cleaned. The cleaning effect in such an arrangement is dependent not only from the pressure of the spray water and the type of the nozzle but also from the distance of the nozzles from the filter cloth. In order to ensure that this distance is maintained constant, in one type of cleaning system the free space on either side of the displaced filter plate is selected to be small and the washing pipe or tube which is provided bilaterally with nozzles, is introduced into the clearance, so that in each instance the two filter plates which define the clearance are simultaneously cleaned.
In a different type of cleaning system, the filter plate to be cleaned is moved towards the open side of the press into a predetermined detached position, so that two washing tubes can straddle the filter plate to be cleaned in a fork-like manner with nozzles directed to one another, so that upon upward and downward movement of the washing tubes, both sides of the filter plate are simultaneously cleaned.
The use of the above-described two cleaning systems is, among others, dependent upon the structure of the filter press stand. In both cleaning systems, however, there are encountered the basic problems of moving the filter plate to be cleaned into an accurate, predetermined position and an accurate control of the washing device. Particularly, an accurate guidance and positioning of the washing device in the clearance at the detached filter plate poses problems, because such free space between the detached filter plate and the filter plate stack on either side thereof continuously changes as the filter plate stack on the closed side is reduced and the filter plate stack on the open side is built up.